Oxidizing of lead to litharge



Patented Sept. 28, 1937 2,094,232'w OXIDIZIN G OF. LEAD TO LI THARGE Robert M; Cole, Bryn Athyn, Pa.

Application August 16, 19 33,

serial No. 685,424 i i'nventi'on rela'tes primarilyto'the oxidiz-' V tionIof causticsoda. and ammoniaf invention will appearfrom the following.

flHeret'ofore, lead has been oxidized tolitliarge by means of sodium nitrate by a process commonly. known as a. dry fusion in, which both the lead and the nitrate are melted and brought into reaction infthefus'ed state. The melting temferature point of lead-is 320 C. and of sodium nitrate 316C. s

The present method departs radically" fromthe above'procedure in that the oxidation'is carried out in a water'environm'ent as', for example, in-an autoclave. By this-newimethod it is-possibleutoproduce lithargeandsodium nitrate (as was the case in the known method above referred to) orlitharge, sodium plumbite, sodium nitrate, caustic soda and ammonia, and this in almost any desired proportion by varying the conditions as will further appear. This difference between the wet and the dry method is to be attributed to the hydrolysis of sodium nitrate. which is a *veak salt.

The method is best performed in a forged steel cylindrical autoclave. If the operation is to be conducted without intermittent opening and closing of the autoclave, the latter is set up in a vertical position with bolted, flanged top and bottom, the molten lead and nitrate solutions being admitted through valves in the. top plate, and the litharge and aqueous products being withdrawn through similar valves in the bottom plate. Where the operation is to be performedwith intermittent opening and closing of the plate, the autoclave is closed at one end and at the other end is provided with a quick opening head. In this case the autoclave is preferably .set up in a horizontal position and the charge is The nature, object's and advantages of the tom valves, thus releasing the pressure.

6 Claims. (01;, 2 3 51) highly surfaced feathered lead. Part oftheboil -t ing Water is removed, and after closing the lead" valve 21. :saturated solution of nitrate ofsoda at: preferably 350 C., is admitted. As the nitrate solution contacts the feathered lead, anexothe'rmic reaction takes place. which gradually raises the temperature of the reacting mass to 300 0., 325 C., or 350-C., as desired, the pressure rang-- ing from approximately 100 to 200 atmospheres. The'temperature is controlled, as for example, 10 by-the rate at which the nitrate solution is in-. troduced, or by the concentration of the nitrate solution, or both.:- The. higher the temperature; the shorter the time of the reaction. By control of the temperature, the kind and amount of end products can be accurately determined. As the time is shortened and the temperature increased, the tendency is toward theexclusive production of theoretical amounts of litharge, caustic soda, and ammonia, part of the caustic soda and litharge being united as sodium plumbite. At lower temperatures and longer time, litharge and sodium nitrate alone are'produced. The preferred range is from about 280 C. to about 350 0.

The solid litharge and caustic soda and ammonia solutions are removed by opening the bot- Removal may be facilitated by the use of steam and water nozzles situated in the bottom of the autoclave. The erosion and flotation incident to r the use of such nozzles readily removes the litharge.

The maximum time necessary is ordinarily approximately thirty minutes.

2nd Procedure-According to the second procedure the molten lead is poured into one of the cartridges immersed in water in a suitable container mounted in a vertical position, thus producing the feathered lead. The cartridge containing the lead is then slid into the horizontal autoclave in much the same manner as in the loading of a gun. The quick opening head is now closed and the nitrate solution admitted as in the first procedure. over the temperature begins to fall, the head is opened and the cartridge removed.

In the above procedures a slight excess of lead is used in the reaction, but this is readily recovered, remaining in the cartridge or autoclave 50' When the reaction is' for re-use. Based on the nitrate, the yield is theoretical for litharge, caustic soda and ammonia, and the process is therefore a useful one as a commercial source for caustic soda and ammonia. The molal heat of the exothermic reaction is two hundred and twenty-nine thousand calories, and therefore quite ample for the evaporation of the caustic soda solution.

Another important advantage and distinction of my process lies in the amount of nitrate of soda required. Whereas the known method required a full molecule of nitrate to furnish sufiicient oxygen for an atom of lead, the new method, theoretically, requires only one-fourth of a molecule of nitrate to bring about the same amount of oxidation in the lead, for the reason that due to the water environment there is the following Because of the oxygen thus made available, a I

little less than one-third of theory for sodium Aside from the appearance of bright new gold which the litharge has while wet, it is also unique in being. formed in water in its original 'state'of subdivision in which it may be retained if desired in paste form.

Because of the above, and for other reasons, the process is more economic and effective.

With respect to the production of litharge for batteries, the process is particularly useful in that it removes impurities such, for example, as copper and manganese, the presence of either of which in small quantities is detrimental. The copper unites with the ammonia to form a cupro-ammonium solution and the manganese unites with caustic soda, both of which can be removed. The reactions are as follows. The first reaction is Pb+NaNO3=PbOtNaNU2 On increase in temperature a second reaction occurs which is as follows:

Adding the first and second reactions the NaNOz cancels out as indicated and we haveshowing that one-quarter of the nitrate is required to bring about the same amount of oxidation in the lead.

When the temperature is such that the second reaction takes place there is also, concurrently, a third reaction as follows:

I claim:

'1. The process which includes pouring molten lead into water to produce feathered lead, and adding sodium nitrate in the presence of water.

2. The process which includes pouring molten lead into water to produce feathered lead, and adding sodium nitrate in the presence of water, heat and pressure.

3. The process which includes reacting lead and sodium nitrate in a vessel containing water and controlling the temperature to produce caustic soda as an end product.

4. The process which includes reacting lead and sodium nitrate in a vessel containing water and controlling the temperature to produce litharge and sodium plumbite as end products,

5. The process which includes reacting lead and sodium nitrate in a water environment at a temperature of from about 280 C. to about 350 C.

6. The process which includes reacting lead and sodium nitrate in a water environment at a temperature of from about 280 C. to about 350 C. and at a pressure from about 100 to about 200 atmospheres.

ROBT. M. COLE.

Patent No. 2,o9h,252.

CERTIFICATE OF: CORRECTION.

September 28, 1957.

ROBERT M. COLE.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, first column, lines 18, 20 and 25, and second vcolumn, 111152 for "nitrate" read 1 nitrite; and that the said Letters-Patent should be read with these cor- 3 rections therein that the same may conform to the record of the case' in the'Patent Office.

Signed aha sealed this 7th day of December, A. D. 1957.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents, 

